1. Field of the Invention
This invention relates to a method of manufacturing high performance cable having a low profile configuration including the steps of drawing conductor subassemblies formed of insulated wire pairs surrounded by an intermediate insulator, through an extruder; forming conductive shields around the subassemblies prior to the extrusion; and extruding an exterior insulator around the shielded subassemblies.
2. Description of the Prior Art
Conventional multiconductor cables for transmitting high frequency electrical signals include both shielded twisted pair cables and coaxial cables. Such cables have their greatest utility in transmitting electrical signals between components of electrical systems. Such transmitted signals are normally in digital form although such transmitted signals may also be in analog form.
Shielded twisted pair cables utilize a pair of insulated conductive wires in a twisted pair configuration with a grounded, electrically conductive shield around each twisted wire pair. The shield functions to reduce electromagnetic interference radiation, generally called EMI, which naturally emanates from signal transmitting wires and which might otherwise adversely affect the performance of adjacent electronic devices. Such shield also functions to minimize cross talk, electrical interference between one pair of wires and an adjacent pair which would tend to impair the fidelity of the signals being transmitted. Shielded twisted pair cables can be used in a differential transmission system where both wires are electrically powered and both constitute signal carrying wires. The information transmitted is a function of the sequential voltage differential between the two wires of the pair. An example of a shielded twisted pair cable is described in U.S. Pat. No. 4,404,424 issued to King et al.
Coaxial cables also use an EMI shield to reduce radiation. But in coaxial cables, unlike shielded twisted pair cables, only one electrically powered signal wire is utilized. The signal wire is encased in insulation which is surrounded, in turn, by the grounded, electrically conductive shield. In coaxial cables, the shield also functions as a grounded reference for the voltage of the signal wire. An example of a coaxial cable is described in U.S. Pat. No. 3,775,552 issued to Schumacher.
Considerable effort has been extended to develop a flat coaxial cable which would yield the same performance characteristics as conventional coaxial cable but which would also enable the use of conventional mass stripping and termination techniques to thus facilitate the coupling of an electrical connector to the cable. Consider for example U.S. Pat. No. 4,488,125 to Gentry et al. Other flat coaxial cables are disclosed in U.S. Pat. Nos. 4,487,992 and 3,775,552.
One application for flat cable is in under the carpet wiring situations in which a flat, low profile cable is extended beneath a carpet for connection to, and coupling of, components of an electrical system such as a computer system or the like. Shielded twisted pair cables do not have a low profile suited for use in undercarpet applications since twisted wires are continuously and sequentially located above, to one side, below, and to the other side of each other along the length of the cable. As a result, the cable thickness periodically increases to a double wire thickness along the length of the cable. This arrangement of signal wires thus precludes low profile cable configurations since low profile cable configurations are possible only in cables having their wires spaced parallel to each other in a single, usually horizontal, plane. The configuration and orientation of wires in a shielded twisted pair cable also precludes mass stripping and termination since the positioning of any one wire with respect to another varies as a function of where the cable is cut along its length.
While many methods of manufacturing electrical cables have been proposed in the past, the instant method is particularly well-suited for the manufacturing of a flat high performance cable, equivalent in performance to a shielded twisted pair cable.